This invention relates to implantable medical devices. Specifically, the invention relates to a system for controlling implantable medical devices.
Implantable medical devices such as ventricular assist devices are being developed for long term treatment of chronic heart failure. Such devices require a pumping mechanism to move blood. Due to the nature of the application, the pumping mechanism must be highly reliable. Patient comfort is also a significant consideration.
Transcutaneous energy transfer (“TET”) systems are used to supply power to devices such as heart pumps implanted internally within a human body. An electromagnetic field generated by a transmitting coil outside the body can transmit power across a cutaneous (skin) barrier to a magnetic receiving coil implanted within the body. The receiving coil can then transfer the received power to the implanted heart pump or other internal device and to one or more batteries implanted within the body to charge the battery.
One of the challenges of such systems is insufficient battery lifetime. The implanted battery may be required to supply the implanted device's entire power demand for one to several hours at a time, such as when the patient does activities that preclude wearing the external TET power unit, such as showering or swimming. When the implanted battery is first implanted into the patient, the battery capacity is large and can meet the power demand for the required amount of time. However, when subjected to frequent charging and discharging, the implanted battery's capacity decreases. With decreased battery capacity, the patient cannot spend as much time without the external TET power unit. Eventually, the battery may need to be replaced so that the patient can go without the external TET power unit for long enough periods of time again.
In addition to the foregoing problems, the use of inductive coils by TET systems to wirelessly transfer power to an implanted battery results in slow recharging times, as inductive charging has lower efficiency and increased heating in comparison to direct contact. Thus, there is a need in the art for ventricular assist device (“VAD”) technology that improves patient lifestyle during internal battery operation (“tether free”) and reduces bulkiness of the external hardware during normal operation. Therefore, there is a need in the art for an implantable component design that solves the problems described above.